Aliphatic polycarbonates are biodegradable eco-friendly polymers. The most appropriate method for mass production of aliphatic polycarbonates is associated with the condensation of dimethyl carbonate (DMC) and various diols (Reaction 1).

DMC has been produced for long time from toxic phosgene. DMC is currently mass-produced at low cost from carbon monoxide or more environmentally friendly carbon dioxide. There are many reports in the literature on the condensation reactions of DMC and diols. However, these reactions are typically slow and have a limitation in increasing the molecular weight of the final polymers. Instead, oligomeric macrodiols whose molecular weight is several thousands and whose ends are all capped with —OH are prepared from DMC and diols, and most of them are used for polyurethane production (EP 302712; EP1874846).
Most efforts to prepare high molecular weight aliphatic polycarbonates have not been successful. Sivaram et al. reported the preparation of aliphatic polycarbonates having a weight average molecular weight of 6,000 to 25,000 by condensation of DMC with various diols using 1,3-diphenoxytetra-n-butyldistannoxane as a catalyst (Polymer Vol. 36, 4851-4854, 1995). U.S. Pat. No. 5,171,830 discloses a process for the preparation of aliphatic polycarbonates including condensing DMC with various diols using a tertiary amine or alkylammonium salt as a catalyst. However, the molecular weights of the polymers prepared by this process are only on the order of 2,400. According to a recent report, an attempt has been made to synthesize aliphatic polycarbonates by condensation of various diols and DMC using 1-n-butyl-3-methylimidazolium-2-carboxylate (1 mol %) as a catalyst. However, the aliphatic polycarbonates have number average molecular weights not higher than 6,700 (Polym. Chem., 2012, 3, 1475). Chuncheng Li only reported the preparation of an aliphatic polycarbonate with a weight average molecular weight of 100,000 or more by condensation of DMC and 1,4-butanediol using a TiO2/SiO2/poly(vinyl pyrrolidone) mixture as a solid catalyst (Polym Int 2011; 60: 1060-1067; Journal of Macromolecular Science, Part A: Pure and Applied Chemistry (2011) 48, 583-594). That is, attempts to prepare high molecular weight aliphatic polycarbonates suitable for use as general-purpose biodegradable plastics are still in the early stages.
Techniques for introducing long-chain branches into polymer chains are of importance in general-purpose plastics, such as polyethylene. The introduction of long-chain branches offers the potential to increase melt-fracture resistance and impart shear-thinning behavior in terms of rheology, ensuring high processability in various applications, such as blown films, cast films, injection molding, blow molding, and thermoforming (Adv. Mater., 2000, 12, 1759; Macromolecules, 2005, 38, 5849).